The disclosure of Japanese Patent Application No. 2000-145310 filed on May 17, 2000, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a continuously variable belt transmission that uses a belt to transmit motive force between two rotary members and, at the same time, controls their gear ratio by changing a winding radius of the belt.
2. Discussion of the Related Art
Generally speaking, a transmission is provided on the output side of an engine with the aim of running the engine in an optimum condition according to vehicle operating conditions. There are two types of such a transmission: a continuously variable transmission that is capable of controlling the gear ratio in a stepless fashion (infinitely variable), and a step variable transmission that can control the gear ratio in several steps (non-continuously). A continuously variable belt transmission is one example of a continuously variable transmission. The continuously variable belt transmission comprises two rotary members disposed in parallel with each other, and a primary pulley and a secondary pulley attached to each of these two rotary members. Each of the primary pulley and the secondary pulley is made up of a combination of a fixed sheave and a movable sheave, and a V-shaped groove is formed between the fixed sheave and the movable sheave.
A belt is wound around the groove in the primary pulley and the groove in the secondary pulley. Hydraulic chambers are provided, each independently generating a pressing force acting in an axial direction on a belt supporting member of the primary pulley and a belt supporting member of the secondary pulley. When the hydraulic pressure of each hydraulic chamber is independently controlled, the width of the groove in the primary pulley is controlled to vary the winding radius of the belt, thus changing its gear ratio. Meanwhile, the width of the groove in the secondary pulley is changed such that the tension in the belt is controlled.
In a continuously variable belt transmission such as that described above, the hydraulic chambers are provided on an outer peripheral side of the rotary members. This could cause an oil pressure generated from a centrifugal force, or what is called the centrifugal hydraulic pressure, to act on the hydraulic chambers, making the hydraulic pressures in the hydraulic chambers higher than the controlled target levels. This results in control accuracy of the groove width supporting the belt being degraded. Japanese Utility Model Publication HEI 02-38555 describes related art pertinent to a continuously variable belt transmission that can solve such a problem.
In the continuously variable belt transmission disclosed in this publication, a secondary pulley (power transmitting member) provided on a secondary shaft (rotary member) is provided with a fixed sheave formed integrally on the secondary shaft and a movable sheave attached movably in the axial direction to the secondary shaft. A cylindrical member that extends in an axial direction toward a side opposite the fixed sheave is formed on the movable sheave. An annular cylinder plate is fixed in position so as not to be movable in the axial direction on an outer periphery of the secondary shaft. An inner peripheral surface of the cylindrical member and an outer peripheral surface of the cylinder plate are in slidable contact with each other, and a first hydraulic chamber is formed between the cylinder plate and the movable sheave. An annular wall is provided on the inner periphery of the cylindrical member and a second hydraulic chamber is formed between the cylinder plate and the annular wall.
In addition, a receiver (oil passage forming member) of cylindrical shape extending in the axial direction toward the cylinder plate side is formed in a rear case that retains the secondary shaft through a bearing. A connecting oil passage is formed between the receiver and a face in the cylinder plate on a side opposite the side of the first hydraulic chamber. The connecting oil passage connects an oil passage provided in the rear case and the second hydraulic chamber.
In a continuously variable belt transmission constructed as described above, a centrifugal hydraulic pressure acts on the first hydraulic chamber while the hydraulic pressure in the first hydraulic chamber is being controlled and, even if the hydraulic pressure in the first hydraulic chamber becomes higher than a target pressure level, a centrifugal hydraulic pressure corresponding to that centrifugal hydraulic pressure acts on the second hydraulic chamber. As a result, the centrifugal hydraulic pressure acting on the first hydraulic chamber and the hydraulic pressure acting on the second hydraulic chamber cancel each other out, which enhances the control accuracy of the groove width of the secondary pulley.
In the continuously variable belt transmission described in above-mentioned publication, the oil passage formed in the rear case and the receiver, which forms a connecting oil passage, is formed on the side of the rear case. For reasons of design and positional relationship, however, it is possible for the oil passage to be formed on the secondary shaft side, the oil passage forming member to be installed on the secondary shaft side, and parts to be installed on both sides of the oil passage forming member in the axial direction. If such a configuration or layout is adopted, the parts disposed on both sides of the oil passage forming member would interfere in the forming of a connecting oil passage for connecting the oil passage of the secondary shaft and the second hydraulic chamber, making the forming thereof difficult. If a new oil passage is disposed so as to bypass the parts on both sides of the oil passage forming member, a new part for bypassing must be provided, thus increasing the number of parts used and requiring more space for mounting parts on the secondary shaft in an axial direction, which may result in vehicle mountability being degraded.
In view of the foregoing problems, it is an object of this invention to provide a continuously variable belt transmission that can supply oil from the side of a rotary member by using an oil passage forming member, without newly installing parts other than oil passage forming parts.
To achieve the foregoing object, a continuously variable belt transmission according to a first embodiment of the invention is provided with a power transmitting member provided on a rotary member, a belt wound around the power transmitting member, a first hydraulic chamber that gives the power transmitting member a holding force to hold the belt in an axial direction of the power transmitting member, a second hydraulic chamber that gives the power transmitting member a force in a direction so as to weaken the holding force, an oil passage through which hydraulic pressure is supplied to the second hydraulic chamber, and an oil passage forming member that is disposed along a path from this oil passage to the second hydraulic chamber. The oil passage forming member is attached to the rotary member, parts disposed on both sides of the oil passage forming member in the axial direction are installed on the rotary member, and the oil passage is provided on the rotary member. In addition, the second hydraulic chamber is connected to the oil passage through a grooved portion provided in the oil passage forming member.
According to a first embodiment, the grooved portion provided in the oil passage forming member itself connects the oil passage and the second hydraulic chamber. This obviates the need for providing a part for exclusive use in connecting the oil passage and the second hydraulic chamber. It further makes it possible to form the grooved portion so as to bypass the parts provided on both sides in the axial direction of the oil passage forming member. The grooved portion in this embodiment may include a cutout portion and a recessed portion.
A continuously variable belt transmission according to a second embodiment of the invention is provided with a belt wound around a rotary member, an oil chamber provided in an area surrounding the rotary member, a bulkhead attached to the rotary member and disposed so as to face the oil chamber, and an oil passage connected to the oil chamber. An oil passage forming member is installed in a space between bearings retaining this rotary member and the bulkhead on an outer periphery of the rotary member. A grooved portion provided in the oil passage forming member constitutes the oil passage.
According to the second embodiment, the oil passage connected to the oil chamber is formed by the grooved portion provided in the oil passage forming member itself. This obviates the need for providing a new part for exclusive use in forming the oil passage. It is also possible to form the oil passage bypassing the bulkhead and bearing. The grooved portion in this embodiment may include a cutout portion and a recessed portion.